Aside

## Sarin learns lines and angles in school (Math Concept)

Lines

Angles

When two straight lines meet or intersecting each other, they form angles.

Two straight lines can only intersect at one point.

To measure angles

The unit of measurement for angle is degree. Symbol: 0

Examples:

90 degree, 900, 300, 450, 1200, 1800, 2700, 3600 etc……

Angles are the measurement of two lines at their intersection point. It is the separation between the two lines that from a reference point.

A protractor is a tool to use for measuring angles.

The angle is 600 measured using a protractor.

A normal protractor can measure angle from 00 to 1800.

What is the angle measure on a straight line?

A circular protractor measure angle from 00 to 3600

The angle indicate in the diagram is 3000

So, a straight line can also measure 3600,

and it  is depends on how the rotation direction indicated.

Different type of angles

An acute angle is an angle measuring between 0 and 90 degrees.

A right angle is an angle measuring 90 degrees.

An obtuse angle is an angle measuring between 90 and 180 degrees.

A reflex angle is an angle measuring greater than 180 degrees.

A straight angle is an angle measuring 180 degrees.

An acute angle or an obtuse angle, with their respective reflex angles measuring 3600.

Two angles are called complementary angles mean the two angles add up gives 90 degrees, or form a right angle.

300 + 600 = 900 which is right angle

300 is complement angle of 600, or

angle 600 is complement of angle 300

Two angles are called supplementary angles mean the two angles sum up gives 1800, or form a straight angle (line).

1200 + 600 = 1800

Angle 1200 is supplement of angle 600

Perpendicular lines

When two lines intersect or meet with an angle measuring 900 or form a right angle, we call the two lines the perpendicular lines.

Line CD meet Line AB at point D

perpendicularly.

Angle ADC = Angle CDB = 900

Line CD intersect Line AB at point E

Perpendicularly.

Angle AEC = Angle CEB = 900

Angle AED = Angle DEB = 900

Vertical angles

If line CD intersects line AB at point E as below, the angle AED measures the same as angle CEB. There are vertical angles.

Same for angle AEC and angle DEB,

angle AEC = angle DEB and there are vertical

angles

Parallel lines

Line AB is said parallel to line CD, if the shorter distance between them is equal as below diagram shown.

The shorter distance is the perpendicular line

that meet line AB and line CD

Line blue, line red and line green

are parallel lines.

Dotted line is perpendicular to all three lines

Line 3 is perpendicular to line 1 and line 2. So line 1 is parallel to line 2.

As line 4 intersect both line 1 and line 2,

we have angle c = angle g and there are corresponding angles.

Similarly,

angle a = angle e and there are corresponding angles.

angle j = angle p and there are corresponding angles. Etc….

Since angle g and angle m are vertical angles,

Angle c = angle m, and there are call alternate interior angles

Similarly, angle j = angle e, and there are call alternate interior angles.

You can also see that,

angle j + angle m = 1800, angle c + angle e = 1800, ext….

angle a = angle p, and there are call alternate exterior angles. Ext….

With another line 5 parallel with line 4 intersectingline 1 and line 2,

you can work out that,

Angle j = angle k, angle n = angle m

Also angle j + angle d + angle m + angle f = 3600 etc….